PORTLAND, Maine — The campaign supporting a November referendum asking voters to allow same-sex marriage contended Friday that a national opposition group is flouting state law by failing to disclose the names of individual donors.

In a campaign finance report, filed Thursday with the Maine Commission on Governmental Ethics and Election Practices, the National Organization for Marriage reported raising and spending more than $250,000 to oppose Question 1, according to Mainers United for Marriage. The report covers the period from July 18 to Sept. 30.

Question 1 would allow same-sex couples to receive a marriage license from the state while protecting religious freedom.

Brian Brown of the National Organization for Marriage, or NOM, called the accusation “absurd.”

Matthew Marett, who works for the ethics commission, which regulates campaign finance laws, said Friday that NOM’s latest report complies with the law.

In a practice that dates back to 2009, NOM refuses to identify the sources of its contributions, the majority of which were funneled to the Protect Marriage Maine PAC, and continues to flout Maine’s campaign finance disclosure laws, Matt McTighe, campaign manager for Mainers United for Marriage, said in a press release issued Friday. Campaign finance laws require disclosure of contributions of more than $50 for PACs and more than $100 for Ballot Question Committees, he said.

Brown said that because the money given to Protect Marriage Maine, which is running the campaign opposing Question 1, came from an undesignated fund, NOM is not required under Maine law to report individual donors.

Brown said the Human Rights Campaign Fund, a national group that supports same-sex marriage, churches and other groups can make contributions in a similar fashion without naming donors.

“The rule is that an organization can transfer general treasury funds on the condition that it didn’t raise the money specifically to influence the Maine campaign,” Marett said. “That appears to be so from the way NOM reported it.”

Neither Protect Marriage Maine nor Mainers United for Marriage had filed reports with the commission as of 4 p.m. Friday.

The criticism of NOM stems from the 2009 people’s veto campaign that repealed the same-sex marriage bill passed by lawmakers and signed by Gov. John Baldacci. During that campaign, NOM did not file as a ballot question committee or provide the names of its donors to the commission, according to a previously published report.

NOM challenged Maine’s campaign finance law in federal court in Portland. In 2010, U.S. District Judge D. Brock Hornby upheld the state’s disclosure laws as they relate to ballot committees. Last year, the 1st U.S. Circuit Court of Appeals agreed with Hornby’s ruling. On Monday, the U.S. Supreme Court declined to take up NOM’s appeal.

The high court’s decision cleared the way for the commission to move forward with an investigation into NOM’s contribution to the 2009 campaign, Jonathan Wayne, executive director of the commission, said Monday. He also said it was premature to discuss possible sanctions against NOM.

David Farmer, spokesman for Mainers United for Marriage, said the organization has not decided whether it would file a complaint with the commission over NOM’s latest report.

Mainers United for Marriage is expected to report raising more than $2.2 million from 8,200 donors during the most recent reporting period, McTighe said in Friday’s press release. So far, the organization has raised a total of $3.4 million from 13,780 donors in its effort to pass the referendum.

More than two-thirds of the contributions to the campaign have come from Mainers and 89 percent of the contributions were for $100 or less, according to Mainers United for Marriage.

Protect Marriage Maine has raised about $414,000, including the $250,000 donation from NOM, Carroll Conley, executive director of the Christian Civic League of Maine, which is donating office space in Augusta to the campaign, said Friday. He said that information about the number of donors to the campaign would not be available until the report is filed late Friday.

The deadline for candidates and groups supporting or opposing referendum questions to file financial information is midnight Friday.